What must you do after attaching a semitrailer?

The correct combination in this scenario involves checking both the fastening and locking system of the fifth wheel, as well as connecting and checking all hoses and cables.

According to German traffic regulations, ensuring the fifth wheel is properly secured prevents the semitrailer from detaching while driving, which could lead to severe accidents. Additionally, hoses and cables are essential for the operation of trailer brakes and other functions. Not checking these components can lead to malfunctions or unsafe driving conditions.

The option to release the reverse lock of the semitrailer is not included in the correct answer because it is not a prerequisite when preparing to drive after attachment. All options that ensure safety and compliance with regulations should be adhered to, emphasizing the importance of thorough checks before hitting the road.